Cyclosporin A inhibits apolipoprotein AI gene expression.

Cyclosporin A (CsA), a calcineurin inhibitor, has been widely used as an immunosuppressant, and is known to induce hyperlipidemia and dyslipoproteinemia with low levels of high-density lipoprotein (HDL). Since apolipoprotein AI (apo AI) is a major protein component of HDL particles and reduction of apo AI results in low levels of HDL, we hypothesized that CsA inhibits apo AI gene expression contributing to its lipid effects. Therefore, we first measured the serum apo AI protein levels in rats with or without CsA treatment, and found that both serum apo AI protein and liver apo AI mRNA levels were significantly reduced in response to CsA treatment. In stably transfected Hep G2 cells harboring an apo AI-474-CAT reporter gene, we found that intracellular calcium mobilization by A23187 a calcium ionophore stimulated apo AI gene expression and the calcineurin inhibitors, CsA and FK605, selectively inhibited this stimulation. Therefore, we conclude that activation of the calcineurin pathway by intracellular calcium mobilization stimulates apo AI gene expression and calcineurin inhibition by CsA results in reduced apo AI gene expression.